Method of and device for the drawing of tubular workpieces

ABSTRACT

A tubular workpiece, to be reduced in diameter and wall thickness, is drawn through a progressively narrowing gap formed between a die and a mandrel coaxial therewith, the die and the mandrel having confronting annular undercuts in an intermediate region of the gap whereby the latter is widened to form storage chambers for lubricant entrained under pressure by the inner and outer surfaces of the advancing workpiece. The lubricant is supplied to the outer storage chamber through a reservoir formed by a sleeve upstream of the entrance end of the die while being also funneled into the inner storage chamber through a narrowing clearance between the tail end of the mandrel and the workpiece. This clearance is surrounded by a converging first die section whose smallest diameter, preceding the undercut, is larger than the exit diameter of a converging second die portion in which the workpiece is shaped to its final dimension; the inner and outer workpiece surfaces are coated with films of lubricant leaving the respective storage chambers. The invention permits to introduction of the plug into the tube unconstrainedly and to obtention an optional small clearance beweeen the plug and the tube, whereby the drawing process operates under conditions of hydrodynamic lubrication. The method of drawing consists in bending the tube around the bearing part of the plug by means of a bearing-working tube drawing die situated immediately in ahead of the working tube drawing die which has a cross section reducing in co-operation with the plug and the tube wall. The plug for application of the method has an initial entry part in the form of a cone and a cylindrical-and-conical part serving for reduction of the tube-wall thickness, behind which a pressing part is situated with at least one pressure-regulating undercut being provided to maintain and to govern the pressure.

States Prajsnar et al.

[ METHUD OF AND DEVICE FOR THE DRAWING OF TUBULAR WORKPIECES [75] Inventors: Tadeusz lPrajsnar; Jozef Rulinski,

both of Gliwice; Edward Zglobicki, Zabrze; Bronislaw Sojka, Zawadzkie, all of Poland [73] Assignee: Instytut Metalurgii Zelaza im. St.

Staszica, Gliwice, Poland [22] Filed: Mar. 17, 1971 [2]] Appl. No.: 125,191

[52] US. Cl. 72/41, 72/283 Primary Examiner-Charles W. Lanham Assistant Examiner-Robert M. Rogers Attorney-Karl F. Ross [57] ABSTRACT A tubular workpiece, to be reduced in diameter and wall thickness, is drawn through a progressively narrowing gap formed between a die and a mandrel coaxial therewith, the die and the mandrel having confronting annular undercuts in an intermediate region of the gap whereby the latter is widened to form stor- 7 bearing-working tube age chambers for lubricant entrained under pressure by the inner and outer surfaces of the advancing workpiece. The lubricant is supplied to the outer storage chamber through a reservoir formed by a sleeve upstream of the entrance end of the die while being also funneled into the inner storage chamber through a narrowing clearance between the tail end of the mandrel and the workpiece. This clearance is surrounded by a converging first die section whose smallest diameter, preceding the undercut, is larger than the exit diameter of a converging second die portion in which the workpiece is shaped to its final dimension; the inner and outer workpiece surfaces are coated with films of lubricant leaving the respective storage chambers.

The invention permits to introduction of the plug into the tube unconstrainedly and to obtention an optional small clearance beweeen the plug and the tube, whereby the drawing process operates under conditions of hydrodynamic lubrication. The method of drawing consists in bending the tube around the bearing part of the plug by means of a drawing die situated immediately in ahead of the working tube drawing die which has a cross section reducing in co-operation with the plug and the tube wall.

The plug for application of the method has an initial entry part in the form of a cone and a cylindrical-and-conical part serving for reduction of the tube-wall thickness, behind which a pressing part is situated with at least one pressure-regulating undercut being provided to maintain and to govern the pressure.

7 Claims, 4 Drawing Figures PATENTED 81974 3,713.63

SHEET 1 or 2 Fig.1

Tadeus z PRAJSNAR Jzef RULINSKI Edward ZGLOBI CKI Bronisiaw SOJKA INVENTORS BY A ATTORNEY PATENTEI] JAN 8 I974 SHEET 2 BF 2 Tadeusz PRQJSNAR Jzef RULINSKI Edward ZGEOBICKI Bronislaw SOJKA INVENTOR 5 ATTORNEY METHOD OF AND DEVICE FOR Til-IE DRAWING OF TUBULAR WORKIPIECES FIELD OF THE INVENTION The invention relates to a plug-drawing method and device for drawing tubes utilizing of the effect of hydrodynamic lubrication with simultaneous reduction of the diameter and the wall thickness of the tube.

BACKGROUND OF THE INVENTION It is known in the of tubes by to bring the bearing part of the plug closer in diameter to the inner diameter of the tube of the tubular workpiece in a converging gap defined by a mandrel or plug and a hollow die coaxially surrounding same.

BACKGROUND OF THE INVENTION Conventional tube-drawing techniques, using floating cylindrical plugs of the self-aligning type, are not conducive to effective lubrication of the workpiece surfaces which are in contact with the mandrel and the die at the outlet of the latter. Also, in many cases, insertion of the mandrel into the tubular workpiece is difficult because of sharp curvature and nonuniform thickness of the tube wall. Limited drawing speeds, excessive wear of the gap-forming surfaces, workpiece failures between the inner surface of the tube being drawn and,

the plug.

In the prior art plug drawing methods for tubes according to the known methods, the insertion of the plug into the tube was very burdensome owing to the considerable curvature of zone tubes and the fact that the wall thickness was not uniform over the length and cross section thereof. Thus the plug could be inserted under the pipe only in laboratory conditions. In industrial attempts only a plug having its diameter considerably smaller than the inner diameter of the tube could be inserted into the tube, thereby in the course of precluding hydrodynamic lubrication. Also the conventional structure of the plug limits the possibilities of using high drawing speeds and of applying high values of individual drafts. Excessive wear and tear of the plug, and failtires of the tube being drawn, and vibrations of the drawing bench represent further disadvantages.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION We realize these objects, in accordance with the present invention, by dividing the die into a first (upstream) section, converging to a minimum diameter less than the original outer diameter but greater than the final diameter of the tubular workpiece, and a second (downstream) section converging to an outlet whose diameter equals the final outer diameter of the workpiece, and by similarly dividing the mandrel or plug into an upstream portion surrounded by the first die section and a downstream portion surrounded by the second die section. The diameter of the preferably cylindrical upstream mandrel portion differs from the minimum diameter of the first or preforming die section, at the point of closest approach, bymore than twice the original wall thickness of the workpiece whereby a narrowing clearance is formed between this upstream portion and the inner workpiece surface; this clearance communicates with a storage chamber, formed by an annular undercut between the two mandrel portions, into which lubricant is admitted under pressure in order to help maintain a film of lubricant on the inner surface of the workpiece in the narrow exit channel at the outlet end of the die where the workpiece is compressed to its final wall thickness.

In a similar manner, the outer workpiece surface is lubricated by providing the die with an annular undercut between its first or preforming section and its second or working section, this second undercut forming another storage chamber for lubricant admitted to it under pressure from an adjoining reservoir.

In accordance with a further feature of our invention, the reservoir for the lubricant coating the outer workpiece surface is formed by a sleeve which adjoins the first die section ahead of its entrance end in spaced relationship with the workpiece passing through the gap.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawing in which:

FIG. ll shows the diagrammatic longitudinal section of a two-stage drawing die according to the invention;

FIG. 2 shows the plug in elevation; and

FIGS. 3 and 4 illustrate modifications of the plug.

SPECIFIC DESCRIPTION In the drawing of tubes according to the invention, the reduction of a tube 1 by the working downstream portion 2 of a mandrel or plug and the surrounding section 3 of a drawing die is preceded by preforrning the tube 1 by a converging upstream die section 4 surrounding a cylindrical plug portion 5. The generally converging gap between the plug and the die leaves a clearance 6 between the inner surface of the tube 1 and the cylindrical plug portion 5 which is so wide as to enable undesired introduction of the plug into the tube.

A cylindrical sleeve 3 adjoining the upstream end of die section 4% is designed to built up pressure of lubricant between the outer surface of the tube and the drawing die 3, 4i. Sealing rings 9 and between die portions 3 and 4 prevent any outward escape of the lubricant.

Sleeve 8 defines with the outer surface of workpiece l a reservoir for lubricant which, as described above, passes between the tube surface and the die and which therefore enters a storage chamber formed by an undercut 19 between the preforming die section 4 and the working die section 3 just beyond a constriction 20 at which die section 4 has its smallest diameter D,. It will be noted that diameter D,, which is larger than the minimum diameter D of die section 3 at the outlet of the die, exceeds the diameter d, of the upstream plug portion 5 by more than twice the original wall thickness of tube 1 so that the clearance 6 forms a passage for the flow of lubricant from the interior of tube 1 to a similar storage chamber 14 defined by an undercut 13 on the plug (between portions 2 and 5 thereof) and the inner tube wall. The plug also has a frustoconical leading end or head 11 and a shank 16 at the opposite end.

The downstream or working portion 2 of the plug may be cylindrical, as illustrated in FIG. 1, or partly frustoconical, as shown in FIGS. 2-4; it can also be provided with a peripheral recess 17, beyond (i.e. downstream of) undercut 14, for the storage of additional lubricant (see FIG. 3). Upstream portion 5 may have several peripheral grooves 18, as shown in FIG. 4, to impede the reverse flow of the lubricant.

In operation, the lubricant present within the tube 1 passes through the clearance 6 formed between the die portion 5 and the inner surface of the tube 1 and collects in the annular undercut l4 and in the modification of FIG. 3 also in the peripheral recess 17 where its pressure reaches high values.

Between the inner surface of the tube 1 and the cooperating plug portion 2 a film of lubricant is formed, maintained by the fluid pressure in space 14 or 17. The bearing portion 5 helps force the lubricant into the groove undercut l4 and stops it from flowing backward with the assistance of grooves 18 in FIG. 4. The outer tube surface is similarly coated with lubricant stored under pressure in chamber 19 as described above.

The method and device according to the invention enable major workpiece deformation at high drawing speeds drawing with smooth running of the tube plug drawing bench.

What we claim is:

l. A method of shaping a tubular workpiece with reduction of its outer diameter and its wall thickness, comprising the steps of:

drawing said workpiece through a generally converging gap between a mandrel and a surrounding die, the die having a first section converging to a minimum diameter less than the original outer diameter but greater than the final outer diameter of the workpiece, the die further having a second section converging to an outlet whose diameter equals said final outer diameter, the mandrel having an upstream portion whose diameter at the point of closest approach of the die differs from the minimum diameter of said first section by more than twice the original wall thickness of said workpiece whereby a narrowing clearance is formed between said upstream portion and the inner workpiece surface in the region of said first section, the mandrel further having a downstream portion whose periphery approaches said second section at said outlet to define therewith an exit channel of a width equaling the final wall thickness of the workpiece, the upstream and downstream portions of said mandrel being separated by an annular undercut forming a storage chamber in communication with said clearance, said first and second sections of the die being separated by an annular undercut forming another storage chamber adjacent the outer surface of the workpiece;

admitting lubricant under pressure into said other storage chamber from a reservoir adjoining said first section; and

admitting lubricant under pressure through said clearance into said storage chamber as the workpiece advances, thereby forming a film of lubricant on the inner surface of the workpiece in said exit channel.

2. A device for shaping a tubular workpiece with reduction of its outer diameter and its wall thickness, comprising:

a hollow die centered on an axis;

a plug coaxially disposed in said die and defining therewith a gap which converges from an entrance end of said die to an exit end thereof, said mandrel and said die being provided with respective annular undercuts in an intermediate region of said gap whereby the latter is locally widened ahead of said exit end to form storage chambers adjacent the outer and the inner surface of a workpiece introduced into said gap; and

supply means for admitting lubricant under pressure to said storage chambers through a relatively wide part of said gap formed between an upstream portion of said mandrel and a confronting first converging die section whereby the inner and outer workpiece surfaces are coated with a film of lubricant in a relatively narrow part of said gap formed between a downstream portion of said mandrel and a confronting second converging die section beyond said undercuts.

3. A device as defined in claim 2 wherein the smallest diameter of said first die section at a constriction ahead of the undercuts is greater than the smallest diameter of said second die section at an exit end of said die, the width of said gap being greater at said constriction than at said exit end.

4. A device as defined in claim 2 wherein said upstream portion is substantially cylindrical.

5. A device as defined in claim 2 wherein said supply means includes a sleeve adjoining said first section ahead of an entrance end of said die and forming a reservoir for the lubricant.

6. A device as defined in claim 2 wherein said downstream portion is provided with a peripheral recess spaced from the undercut of said mandrel.

7. A device as defined in claim 2 wherein said upstream portion is provided with at least one peripheral groove spaced from the undercut of said mandrel. 

1. A method of shaping a tubular workpiece with reduction of its outer diameter and its wall thickness, comprising the steps of: drawing said workpiece through a generally converging gap between a mandrel and a surrounding die, the die having a first section converging to a minimum diameter less than the original outer diameter but greater than the final outer diameter of the workpiece, the die further having a second section converging to an outlet whose diameter equals said final outer diameter, the mandrel having an upstream portion whose diameter at the point of closest approach of the die differs from the minimum diameter of said first section by more than twice the original wall thickness of said workpiece whereby a narrowing clearance is formed between said upstream portion and the inner workpiece surface in the region of said first section, the mandrel further having a downstream portion whose periphery approaches said second section at said outlet to define therewith an exit channel of a width equaling the final wall thickness of the workpiece, the upstream and downstream portions of said mandrel being separated by an annular undercut forming a storage chamber in communication with said clearance, said first and second sections of the die being separated by an annular undercut forming another storage chamber adjacent the outer surface of the workpiece; admitting lubricant under pressure into said other storage chamber from a reservoir adjoining said first section; and admitting lubricant under pressure thrOugh said clearance into said storage chamber as the workpiece advances, thereby forming a film of lubricant on the inner surface of the workpiece in said exit channel.
 2. A device for shaping a tubular workpiece with reduction of its outer diameter and its wall thickness, comprising: a hollow die centered on an axis; a plug coaxially disposed in said die and defining therewith a gap which converges from an entrance end of said die to an exit end thereof, said mandrel and said die being provided with respective annular undercuts in an intermediate region of said gap whereby the latter is locally widened ahead of said exit end to form storage chambers adjacent the outer and the inner surface of a workpiece introduced into said gap; and supply means for admitting lubricant under pressure to said storage chambers through a relatively wide part of said gap formed between an upstream portion of said mandrel and a confronting first converging die section whereby the inner and outer workpiece surfaces are coated with a film of lubricant in a relatively narrow part of said gap formed between a downstream portion of said mandrel and a confronting second converging die section beyond said undercuts.
 3. A device as defined in claim 2 wherein the smallest diameter of said first die section at a constriction ahead of the undercuts is greater than the smallest diameter of said second die section at an exit end of said die, the width of said gap being greater at said constriction than at said exit end.
 4. A device as defined in claim 2 wherein said upstream portion is substantially cylindrical.
 5. A device as defined in claim 2 wherein said supply means includes a sleeve adjoining said first section ahead of an entrance end of said die and forming a reservoir for the lubricant.
 6. A device as defined in claim 2 wherein said downstream portion is provided with a peripheral recess spaced from the undercut of said mandrel.
 7. A device as defined in claim 2 wherein said upstream portion is provided with at least one peripheral groove spaced from the undercut of said mandrel. 